In recent years, gas supply facilities equipped with a so-called pressure type flow controller to be used for a gas supply facility to a process chamber have been widely used.
An example is illustrated in FIG. 8. It is so constituted that pressure type flow controllers C1, C2 and C3 and fluids switching valves D1, D2 and D3 are provided with a gas supply facility, and switching of fluids supplied to a process chamber E and flow rate adjustments are automatically performed by signals from a controller B (TOKU-KAI-HEI No. 11-212653 and others).
It is so constituted that, with the aforementioned pressure type flow controllers C1, C2 and C3, a flow quantity Qc passing through an orifice is computed with a formula Qc=KP1 by a computation device M by maintaining fluids pass through an orifice Ka under critical conditions (P1/P2 larger than approx. 2) as illustrated in FIG. 9, to open or close a control valve V (to regulate pressure P1 on the upstream side of an orifice) so that the difference Qy with a set flow rate Qs is made to be zero. Here, A/D designates a signal converter, and AP designates an amplifier (TOKU-KAI-HEI No. 8-338564).
As shown in FIG. 10, the internal pressure of the aforementioned process chamber E is maintained at a set value (10−6-102 Torr) by continuously operating vacuum pumps VP1 and VP2 through an evacuation line Ex having a comparatively large bore equipped with an automatic pressure controller APC and a conductance valve CV.
A combination of a primary vacuum pump (a high vacuum pump) VP1 such as a turbo molecular pump and the like and a secondly vacuum pump (a low vacuum pump) VP2 such as a scroll pump and the like is widely employed for the aforementioned vacuum pump while an exhaust system for which one pump having a large exhaust volume and a large compression ratio is used has a disadvantage in manufacturing costs and the like, so it is not popular.
A fluids supply facility to a chamber shown in FIG. 8 has characteristics that pressure type flow controllers C1-Cn used for the facility are not influenced by internal pressure changes on the side of the chamber E. Therefore, the facility which allows comparatively stable control on the flow rate of the supply gas achieves an excellent, practical effect even with internal pressure changes of the chamber as long as critical conditions are maintained.
However, there are found various difficulties with this type of fluids supply facilities. Among these difficulties, to improve flow rate control accuracy in a small flow quantity range is the one which is needed to be solved urgently.
For example, on the assumption that flow rate control accuracy of a pressure type flow controller which rated flow rate is 1 SLM (the gas flow rate converted to a standard state) is set at 1% F.S. in a setting of less than 10%, there may be a possibility that an error of a maximum of 1 SCCM with the control flow rate value of a set 1%. Accordingly, when the control flow rate becomes less than 10% of the rated flow rate (for example, less than 10-100 SCCM), influence of the error of the aforementioned 1 SCCM cannot be ignored. As a result, an accurate flow rate control cannot be expected in a small flow quantity range of less than 100 SCCM.
With the process chamber E in the afore-shown FIG. 10, continuous operation of a primary pump VP1 and the like such as a turbo molecular pump and the like having a high compression ratio and a large exhaust volume is needed.
Furthermore, to reduce loads of the primary vacuum pump VP1 and the secondary vacuum pump VP2, it becomes necessary that a diameter of the pipe for an evacuation line Ex needs to be relatively large. In addition, a conductance valve CV, an automatic pressure controller APC and the like are required. Accordingly, equipment costs of a vacuum chamber E go high, and the reduction of the costs becomes difficult to be achieved.
Patent Literature: TOKU-KAI-HEI No. 11-212653
Patent Literature: TOKU-KAI-HEI No. 8-335846